This invention relates to mass properties measurement systems. More particularly, it relates to a controlled drive for controllably driving a mass properties measurement system in rotation.
The inertial properties of a body depend on its mass and mass distribution. Measurements of these properties allow the engineer to determine the principal axes, moments and products of inertia so as to predict its behavior under free body or driven (constrained) motion. Especially in the area of spacecraft development and construction, it has become increasingly important to accurately determine the inertial properties of the spacecraft and its payload.
Current trends in spacecraft design are toward non-rigid construction. The distributed mass properties are not constant and therefore require measuring the dynamic characteristics versus frequency. Some of such measurements, e.g., the determination of products of inertia, require that measurements be made while the object is rotating at a constant speed. With the payload mounted on a vertical dynamic balancing machine, for example, rotation of the load permits measurement of the moments reacting on the spindle bearings.
One such mass properties measurement system is described in Carpenter, David A., "Instrumental Gas Bearings Provide A Test Bed For High Accuracy Inertia (Moments & Products) Measurements", SAWE Paper No. 113, Index Category No. 6.0, presented at the 35th Annual Conference of the Society of Allied Weight Engineers, Inc., Philadelphia, Pa., May 24-26, 1976 (hereafter the "Carpenter paper"); the disclosure of the Carpenter paper is incorporated herein by reference thereto.
Heretofore known systems have utilized arrangements such as a DC motor driving the object and measurement table through, e.g., a belt drive and magnetic clutch arrangement. One such mechanism is described in McCullough, Clarence H. "A Method Of Automated Dynamic Balancing", Paper No. 719, presented at the 27th Annual Conference of the Society of Aeronautical Weight Engineers, Inc. at New Orleans, La., May 13-16, 1968 (hereafter the "McCullough paper"); the disclosure of the McCullough paper is incorporated herein by reference thereto.
In addition to being bulky and complex, such previously known drive systems also had a tendency to impart extraneous forces to the system, thereby reducing the accuracy of measurements made on the test object. It was also difficult to maintain the accuracy and constancy of the speed of such systems.
It is a principal object of the present invention to overcome such disadvantages of heretofore known drive systems.
It is a further object of the invention to provide a mechanism for rotatably driving a mass properties measurement system whereby the drive system is and remains substantially invisible to the measurement system.
It is a still further object of the invention to provide a mechanism for rotatably driving a mass properties measurement system in which the drive mechanism can accurately maintain and/or adjust the rotational speed of the measurement system such that during said maintenance and/or adjustment periods, the drive mechanism remains substantially invisible to the measurement system.